Stepping motors are capable of being precisely controlled in rotation angle and rotation speed when supplied with computer-controllable pulse signals, so that these motors are used extensively as the mechanism drive source primarily in the field of precision apparatus. For example, automated analyzers that perform qualitative and quantitative analyses of specific components in biological samples such as blood or urine have a mechanism in which the stepping motor is used to drive the plunger of a liquid dispensing syringe so as to suck or deliver predetermined amounts of biological samples, reagents, and their reaction liquids through a liquid dispensing nozzle or the like connected with the syringe via a flow channel.